Most internal combustion engines have some type of emission control devices. One type, common to many engines, is recirculation of exhaust gas from an exhaust system to an intake system of the engine. A high pressure EGR system recirculates exhaust gas typically from upstream of a turbine, or other similar device, to downstream of a compressor. Other systems recirculate gas at a low pressure, and are called low-pressure systems. An engine having a high-pressure EGR system has a junction somewhere in the air intake system where EGR gas and intake air mix to form a mixture. The mixture of exhaust gas and intake air is consumed during engine operation.
Providing each cylinder of an internal combustion engine with a homogeneous mixture of exhaust gas and air is advantageous for operation. A homogeneous mixture promotes efficient operation of the engine because the emission and power output of each cylinder is uniform. The homogeneity of the mixture provided to each cylinder becomes a design parameter of special importance for engines running a considerable amount of EGR over a wide range of engine operating points.
Many methods devised in the past were intended to improve mixing of exhaust gas with intake air for engines having an EGR system. These methods typically use flow obstructions that increase turbulence in the intake air, the exhaust gas, or the mixture of intake air and exhaust gas, to improve the homogeneity of the mixture supplied to the engine's cylinders. Such methods, although typically fairly effective, have the disadvantage of increasing pressure losses in the intake system of the engine as a result of increased turbulence in the intake air or in the intake mixture. Increased pressure losses in the intake system of an engine leads to decreased engine efficiency and increased fuel consumption.
Accordingly, there is a need for effective mixing of exhaust gas with intake air in an engine having an EGR system that does not decrease the engine efficiency or increase fuel consumption.